1. Field of the Invention
The invention relates to a door latching system and particularly to one having a combined latch and operator for use with the doors of heated cavities, such as microwave ovens.
2. Description of the Prior Art
This invention was especially designed for a door latching system for a microwave oven that has the added convenience of a pyrolytic self-cleaning oven cycle by use of radiant heating means. It is imperative that a microwave oven have its door latched closed during its operation so as to prevent the leakage or direct exposure to microwave radiation from within the oven cooking cavity. When the oven door is unlatched and opened, the microwave energy is first automatically deenergized within the oven. There is a similar latching requirement for pyrolytic self-cleaning ovens; that is, the oven door must be closed and latched shut during the cleaning cycle, especially at temperatures above about 600.degree.F as is explained in the U.S. Reissue Pat. No. Re. 26,944 of Clarence Getman, which is assigned to the assignee of the present invention. The microwave oven door may be unlatched at any time in the operation of the oven, but a self-cleaning oven should not be capable of being unlatched until the oven temperature drops below about 600.degree.F. Thus the latching mechanism in its self-cleaning mode is provided with a locking means.
The present invention is a modification of the latch mechanism that is described in U.S. Pat. No. 3,750,643 of Roland V. Fowler, James A. White and David C. Cross, which is assigned to the present assignee. This patented latch mechanism is a three position latch having a pivoted handle with an extreme unlatched position, an intermediate latched position for microwave operation, and an opposite extreme latched position that is locked during the self-cleaning cycle. Because the handle of this patented latch mechanism has an intermediate position, it would in this intermediate position ordinarily protrude from the front of the oven and create a hazard. The patented latch mechanism has a special pivot arrangement for providing the outermost end of the latch handle with a flattened arc of travel so it does not constitute an obstruction in its intermediate position.
The present invention has greatly simplified the latch construction by converting it to a two position latch mechanism having three functions or modes. An electroresponsive means is employed to discriminate between the latched and the latched/locked functions.
It has been found expedient to provide separate door interlock switches and circuits for operation during the latched functions and the latched/locked function for discriminating between the microwave cooking operation and the pyrolytic self-cleaning oven cycle so as to simplify the control circuits and reduce the total cost of electrical components.